Question: The area of a rectangle is $42$ square millimeters. The length is $7$ millimeters. What is the perimeter of the rectangle?
Answer: Area is the amount of space a flat shape fills. $\text{Area of a rectangle} = \text{width} \times \text{length}$ The ${\text{area}}$ of the rectangle is ${42}$ square millimeters and the ${\text{length}}$ is ${7}$ millimeters. $7\text{ mm}$ $7\text{ mm}$ $$ $w$ $w$ $42\text{ millimeters}^2$ $\begin{aligned} {\text{area}} &= {7}\times{w}\\\\ {42} &= {7}\times{w}\\\\ {42}\div7&={w}\\\\ 6&={w} \end{aligned}$ Now, we can find the perimeter. $\begin{aligned} \text{Perimeter} &= {\text{ length}} + {\text{ width}} + {\text{ length}} + {\text{ width}}\\\\ &=7 + 6 + 7 + 6\\\\ &=26 \end{aligned}$ The perimeter of the rectangle is $26$ millimeters.